It is well known that both negative energy balance and muscle catabolism are consequences of physiological/metabolic stress that often accompanies protein calorie malnutrition, strenuous physical exercise, physical trauma, burn injury, surgical trauma, malnutrition, maldigestion, malabsorption, hyperthyroidism, chemotherapy, radiation therapy, anorexia, cachexia, short bowel syndrome, especially in people of older age. It is also known that maintaining a positive metabolic energy balance can help to alleviate such problems.
During severe stress, regardless of the initiating cause, there is an important mobilization of amino nitrogen from skeletal muscle and connective tissue to support the synthesis of visceral and acute phase proteins. This metabolic response, which is best understood as a redistribution of nutrients from reserves to more active tissues for host defense and recovery, results in the acceleration of protein degradation and an elevation of energy expenditure. In addition, muscle protein catabolism provides the precursors for oxidation of branched chain amino acids and the synthesis and release of alanine for hepatic metabolism as a glyconeogenic substrate. Urinary nitrogen excretion is often elevated and the organism suffers negative nitrogen balance.
However, this adaptive procedure is often insufficiently effective in cases of severe stress or injury, such as surgery, infections, thermal injury, chronic infections, and the final stages of cancer and AIDS, where net loss of lean body mass may exceed 500 g/day (15-20 g urinary nitrogen excretion/day). This decreased ability of injured or infected organisms to utilize amino acids for protein synthesis is a contributing factor in the increased risk of morbidity and mortality that is observed in seriously ill patients. If the stress or injury is persistent, nitrogen losses will eventually deplete the body's protein pool and this catabolism will compromise critical functions resulting in a progressive deterioration of lean body mass and increased risk of severe complications that eventually may lead to death.
Stress or injury such as some forms of surgery and some traumata is often accompanied by partial or complete dysfunction of the gastro-intestinal tract. Patients suffering from such dysfunction or who are subject to disuse of the gastro-intestinal tract because of physician's prescription are obliged to receive most or all of their daily nutritional requirements parenterally and/or orally (including tube feeding). To avoid losses in lean body mass in patients who have suffered serious injury or trauma, it is common practice to supplement compositions used for enteral or parenteral feeding (infusion solutions) with amino acids to replace the amino acids secreted by the lean body mass. A typical nutritional infusion solution comprises an aqueous solution of carbohydrates, fats and amino acids. However, even when amino acids are parenterally administered with an infusion solution, a negative nitrogen balance is still often encountered over a sustained period of time, with a concomitant reduction in lean body mass, though the negative nitrogen balance might not be as severe as it would be in the absence of the infused amino acids. Thus, the period of time that parenteral feeding can be utilized as a sole means of nutrition is extended by the use of amino acids, but for many illnesses, the period is not extended sufficiently to avoid the serious effect of a prolonged net negative nitrogen balance.
A typical nutritional formula for enteral use will provide high amounts of protein and much energy per gram of product. However, such formulae are often ineffective in reversing net catabolism, even though they are sometimes capable of delaying net catabolism to some extent. The high density of nutrients causes several problems, including an adverse effect on taste and product stability. This is particularly important for patients suffering from metabolic stress who, due to their disease, suffer from reduced appetite and who generally are capable of consuming only relatively small amounts of food or drinks.
An anabolic response is desired during growth. Especially infants, in particular premature infants need effective nutritional support to achieve rapid weight gain and to increase life expectations.
Also sportsmen aim to increase their lean body mass in order to increase performance or because of cosmetic reasons. In order to achieve this, typically large amounts of protein, energy and other components are consumed, which may impart their natural dietetic benefits and therefore nutritional status. Typically, these products are dominant in protein, especially those from dairy origin.